Everything was working perfectly a few hours ago, l I shut down normally and just turned on PC. I can't access any SSL sites, I always get security certificate errors and warnings about safety. Windows Update doesn't work, it says it has not been updated in 30 days - which is false since I just checked last night. My anti-virus stopped working and kept saying it was outdated, also not possible. I tried to uninstall but couldn't, so had to do it via safe mode using the ESET uninstaller tool in command prompt. Support has no info, I don't know what else to do and really really x100 don't want to have to reformat/clean install! Is this a known issue? Perhaps with ESET?

I don't recall seeing any mentions of a widespread problem like this on ESET's support forum, but, then again, I don't visit it daily.

My initial thought is that something damaged the installation of your ESET software, either a benign software update to something else, or something malicious like an infection of Win32/Sirefef (a/k/a ZeroAccess).

I am not sure which of those it might be, but in either case, my solution would be the same: Give their support a call at +1 (866) 343-3738 and ask them to walk you through troubleshooting the reinstallation of the software. They should be open from 9:00AM - 9:00PM EST, so you should be able to get a hold of someone during the day fairly easily.

It didn't, so I just wiped and reinstalled W8 using the Home 64-bit disc from Dell. I went to PowerShell to verify Secure Boot via the confirm-SecureBootUEFI command and it said false. I double checked Secure Boot is ON and Boot Mode is UEFI in BIOS. BIOS has a new option under Secure Boot control, Clear Secure Boot Database but it is inaccessible. What to do to install W8 with Secure Boot ON?

It didn't, so I just wiped and reinstalled W8 using the Home 64-bit disc from Dell. I went to PowerShell to verify Secure Boot via the confirm-SecureBootUEFI command and it said false. I double checked Secure Boot is ON and Boot Mode is UEFI in BIOS. BIOS has a new option under Secure Boot control, Clear Secure Boot Database but it is inaccessible. What to do to install W8 with Secure Boot ON?

To be honest if you don't know how to change UEFI to get Secure Boot up and running it's probably not worth doing! The situation you have here would seem to be malware of some type however as some users pointed out, your time was wrong and as you may or may not know the server allocated certificates check system time to check synchronicity for expiration. If you ever do get a problem like this again then I advise using the "Reset PC" option in Windows 8 PC settings menu or advanced options at the graphical/BW system options if you can't get a clean boot.

PS you don't want to clear the database because that has the keys in it!